Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-09-29
2003-07-01
Chin, Vivian (Department: 2682)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S332000
Reexamination Certificate
active
06587447
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field:
The present invention relates in general to Code Division Multiple Access (CDMA) systems and in particular to a Dedicated Control Channel (DCCH) and a Supplemental Channel (SCH) in a CDMA system. Still more particularly, the present invention relates to a method and system for controlling power in a DCCH and a SCH of a CDMA system operating in Discontinuous Mode (DTX).
2. Description of the Related Art:
The fast growth in the use of wireless means of communication has resulted in a complex process for world wide frequency allocations and a number of frequency allocation protocols. Code Division Multiple Access (CDMA) is one of the distinct digital channel sharing topologies which have emerged as a result of a growing need for more channels or more efficient use of channels in digital communication. In a typical CDMA system, a honeycomb type pattern of cells is created which utilizes the same range of radio frequencies. CDMA systems can utilize precisely the same frequency spectrum in all sectors. This allows a single frequency to serve multiple users. The CDMA air interface is very efficient in its use of the subscriber station transmitter power, enabling the widespread commercial use of low cost, lightweight, hand-held portable units that have vastly superior battery life. The technology is also very efficient in its link budgets, minimizing the number of base stations required for an excellent grade of service coverage. Also, CDMA's use of soft handoff (occurring when a user passes across a cell boundary) nearly eliminates the annoyance of dropped calls, fading, and poor voice quality.
The specifications for CDMA operation are outline in the Electronic Industries Association/Telecommunications Industry Association (EIA/TIA) IS-95-A & TSB74 standards document entitled Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System or
CDMA Principles of Spread Spectrum Communication
, by Andrew J. Viterbi. Recent developments in CDMA technology have led to the development of the IS-2000 standard to replace the traditional IS-95 standard.
The cdma2000 family of standards specifies a spread-spectrum radio interface that uses CDMA technology to meet the requirements for third generation (3 G) wireless communication systems. Development of the cdma2000 family of standards has, to the greatest extent possible, adhered to the current architecture by specifying different layers in different standards. The physical layer is specified in IS-2000-2, the Medium Access Control (MAC) layer in IS-2000-3, the Link Access Control (LAC) layer in IS-2000-4, and upper layer signaling in IS-2000-5. The standards in the family correspond to the CDMA layers, and include:
IS-2000-1 Introduction to cdma2000 standards for spread spectrum systems
IS-2000-2 Physical Layer Standard for cdma2000 spread spectrum systems
IS-2000-3 Medium Access Control (MAC) Standard for cdma2000 spread spectrum systems
IS-2000-4 Signaling Link Access Control (LAC) Standard for cdma2000 spread spectrum systems
IS-2000-5 Upper Layer (Layer 3) Signaling Standard for cdma2000 spread spectrum systems
In addition, the family includes a standard that specifies analog operation, to support dual-mode mobile stations and base stations:
IS-2000-6 Analog Signaling Standard for cdma2000 spread spectrum systems
During normal operation, CDMA systems utilize frame transfer by which data is stored and transferred in a frame protocol format. Each frame has an associated power control block of bits which assist in ensuring that the signals are transmitted with sufficient power to be recognized at the receiver end for a given Grade of Service (GOS). As a CDMA phone is transmitting, the receiving cell site is constantly measuring the signal strength of the transmission. When the signal weakens, the transceiver in the cell site transmits power control up commands to the phone, instructing it to increase its power. If the signal strengthens, power control down commands instruct the phone to decrease its power.
The IS-95 standard, defines procedures for a complex power control method, designed to save on battery life and help prevent co-channel interference. The IS-2000 standard has been introduced to replace the IS-95 standard and incorporates many of the power attributes of its predecessor. Throughout the remainder of this document, use of the term CDMA, cdma2000 or IS-2000 refers to the cdma2000 family of standards.
In IS-2000, power considerations are important for efficient use of the system. Thus, the IS-2000 standard includes a dedicated control channel (DCCH). Assuming an efficient power control method, the use of DCCH can provide up to 3.8 dB gain when no data is being sent. This gain is a result of discontinuous transmission (DTX). When there is no data to send, DCCH is able to stop transmitting everything but power control bits in frames, while the fundamental channel (FCH) has to transmit eighth rate frames. However, the DTX transmission on DCCH may often degrade the performance of outer loop power control (i.e., the mechanism which adjusts the target Eb/No on a per frame basis) on both the forward and reverse links. This decreases the potential gain achievable from the use of the DCCH and may result in a performance penalty.
Thus, two major problems exist in the use of DCCH in DTX mode. These are (1) problem in outer loop power control resulting in reduced capacity, and (2) possible call drop. Both problems stem from the receiver's inability to distinguish between an erroneous frame and a cessation of transmission. In normal operating modes, when a frame error is detected at the Receiver Station, the receiver increases the target bit energy to noise spectrum density ratio (Eb/No). Otherwise, the target signal power level (Eb/No) is decreased. However, during DTX period, only power control bits are transmitted. In this case, the receiver is not able to distinguish between an error frame and a cessation of transmission . The misinterpretation of a transmission stoppage as a bad frame causes the receiver to increase its target Eb/No, and thereby commands the transmitter to power up unnecessarily. If the transmitter is smart enough, it can ignore this power up command as it knows it is in DTX mode. However, when the data transmission resumes, the target Eb/No at the receiver is too high Consequently, the transmitter is forced to transmit data at a higher power level than necessary. In addition, the mobile unit stops transmission on the reverse link if it receives twelve consecutive erroneous frames on the forward link and it drops the call if there are no two consecutive good frames during any five second period Therefore, DTX on the DCCH may also lead to possible call drops if no detection is used to determine when DTX is on or off.
Samsung has proposed two methods of frame error estimation of DCCH in DTX mode to try to solve the outer loop power control problem. These methods focus on the forward link and estimate the forward link error of the DCCH in DTX. The methods are summarized below.
1. Mobile System (MS) measures the average Eb/No using power control bits over a frame and maps it into frame error rate (FER) using a lookup table made from the additive white gaussian noise (AWGN) channel with a pre-determined offset value. Then the MS determines frame error in a stochastic way, i.e., generating a random number uniformly distributed over [0, 1] and comparing it with the FER. If the random number is larger than the FER, then the received frame is considered as a good frame. Otherwise, a frame error occurs.
2. MS measures the average Eb/No power control bits over one frame duration and compares the average Eb/No with the certain threshold value. If the average Eb/No is less than the threshold, the frame is considered bad. Otherwise the frame is considered good.
One obvious drawback with both methods is that while they may work well with a particular case for which they are optimized (eg., a particular MS speed and a channel
Chheda Ashvin
Paranchych David
Wang Yiping
Bracewell & Patterson L.L.P.
Chin Vivian
Crane John D.
Nortel Networks Limited
Ramos-Feliciano Eliseo
LandOfFree
Method and system for performing outer loop power control in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and system for performing outer loop power control in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and system for performing outer loop power control in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3040367